I have seen many holding a so called ergonomic holder in a tripod or modified tripod grip , which beats the whole propose of using an ergonomic holder.
When it comes to an ergonomic calligraphy holder , every calligrapher seems to want one. It was commonly and usually wrongfully assumed that an ergonomic holder will help in writing for longer duration without hurting one carpels and metacarpals. Which might be true provided you are holding these holders as they are supposed to be held.
For the purpose of understanding this post, Lets just be clear on what we mean by an ergonomic holder…

So what’s the right purpose?
Let us start from the top… The purpose of using of an ergonomic holder is to HELP you hold the writing tool in the right way to get the best out of it and in the process reducing the stress on your hands (wrist, arm, palm), hence enabling you to write better and longer.
When should I use an ergonomic holder?
The ergonomic holders are primarily designed to write with a hold that is termed as “Knuckles Up Writing” . You can easily practice knuckles-up writing with a regular hourglass or a pencil/pen grip kind of oblique holder too. Only, using a ergonomically shaped holder kind-of reminds you or forces you to write with knuckles-up. One needs to practice kncukles-up form of writing ( as opposed to more traditional tripod grip) when you are into Spencerian and Engrosser hands of writing.
If you are into modern calligraphy or any free hand variety of pointed pen calligraphy, then one should not be using an ergonomic holder. Rather, its easier to do to modern calligraphy using a straight holder.

Thumb Position
The best position to place your thumb while using an ergonomically shaped is behind the flange. If you are used to resting your thumb over the flange then ergonomic holder might not be right for you.

Summary
- Most of the vintage holder shapes Skeels, Gmeiner , Ransomerian, Strahm etc. are ergonomic holders primarily designed for Knuckles-Up writing of cursive hands such as Spencerian, Palmers , Madarasz etc.
- An hourglass shaped holder is also an ergonomic holder
- If you are in a habit of holding the writing tool in a tripod or similar grip , then rework your grip to use a ergonomic holder OR avoid using a ergonomic holder
Disclaimer
All that I have said above , is from personal experience only. I am sure there will be experts who might feel otherwise and will have a more experienced understanding. Feel free to leave your comments.